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{{short description|Order of insects}}
{{About|the insect|the process of flying|Flight|and|Flying (disambiguation){{!}}Flying|other uses}}
{{Redirect|Flies}}
{{Good article}}
{{Pp-semi-indef}}
{{Use dmy dates|date=May 2016}}
{{Automatic taxobox
| fossil_range = {{Fossil range |245|0}}<small>Middle [[Triassic]] – Recent</small>
 | image         = File:Bessenbandzweefvlieg Vrouwtje (2).JPG
 | image_caption = ''[[Syrphus ribesii]]'', showing characteristic dipteran features: large [[eye]]s, small [[antenna (biology)|antennae]], [[Morphology of Diptera|sucking mouthparts]], single pair of flying [[wing]]s, hindwings reduced to clublike [[haltere]]s
| display_parents = 2
| taxon = Diptera
| authority = [[Linnaeus]], [[10th edition of Systema Naturae|1758]]
| subdivision_ranks = Suborders
| subdivision = [[Nematocera]] ([[paraphyletic]]) (inc [[Eudiptera]])<br/>[[Brachycera]]
}}
[[File:Anthomyiidae (female) (10144905255).jpg|thumb|266px|An [[Anthomyiidae|Anthomyiid]] species showing characteristic dipteran features: large [[eye]]s, small [[antenna (biology)|antennae]], [[Morphology of Diptera|sucking mouthparts]], [[Diptera wing|single pair of flying wing]]s, hindwings reduced to clublike [[halteres]]]]

'''Flies''' are [[insect]]s of the [[Order (biology)|order]] '''Diptera''', the name being derived from the [[Ancient Greek|Greek]] δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced mechanosensory organs known as [[halteres]], which act as high-speed sensors of rotational movement and allow dipterans to perform advanced aerobatics. Diptera is a large order containing more than 150,000 [[species]] including [[horse-flies]],{{efn |Some authors draw a distinction in writing the common names of insects. True flies are in their view best written as two words, such as [[crane fly]], [[robber fly]], [[bee fly]], [[moth fly]], and fruit fly. In contrast, common names of non-dipteran insects that have "fly" in their names are written as one word, e.g. butterfly, stonefly, dragonfly, scorpionfly, sawfly, caddisfly, whitefly.<ref>{{cite web |url=https://bugguide.net/node/view/55 |title=Order Diptera: Flies |website=BugGuide |publisher=[[Iowa State University]] |access-date=26 May 2016}}</ref> In practice, however, this is a comparatively new convention; especially in older books, names like "saw fly" and "caddis fly", or hyphenated forms such as [[house-fly]] and dragon-fly are widely used.<ref name="Comstock 1949">{{cite book |last=Comstock |first=John Henry |author-link=John Henry Comstock |title=An Introduction to Entomology |publisher=Comstock Publishing |date=1949 |page=[https://archive.org/details/introductiontoen1949coms/page/773 773] |url=https://archive.org/details/introductiontoen1949coms}}</ref> Exceptions to this rule occur, such as the [[hoverfly]] (though some authors prefer "hover fly"<ref>{{Cite Q|Q96245622|page=15}}</ref>), which is a true fly, and the [[Lytta vesicatoria|Spanish fly]], a type of [[blister beetle]].}} [[crane flies]], [[hoverflies]], [[mosquito]]es and others.

Flies have a mobile head, with a pair of large [[compound eye]]s, and mouthparts designed for piercing and sucking (mosquitoes, black flies and robber flies), or for lapping and sucking in the other groups. Their wing arrangement gives them great manoeuvrability in flight, and claws and pads on their feet enable them to cling to smooth surfaces. Flies undergo complete [[metamorphosis]]; the eggs are often laid on the larval food-source and the larvae, which lack true limbs, develop in a protected environment, often inside their food source. Other species are [[ovoviviparous]], opportunistically depositing hatched or hatching larvae instead of eggs on [[carrion]], dung, decaying material, or open wounds of mammals. The pupa is a tough capsule from which the adult emerges when ready to do so; flies mostly have short lives as adults.

Diptera is one of the major insect orders and of considerable [[ecological]] and human importance. Flies are major pollinators, second only to the bees and their [[Hymenoptera]]n relatives. Flies may have been among the evolutionarily earliest pollinators responsible for early plant [[pollination]]. [[Drosophila|Fruit flies]] are used as [[model organism]]s in research, but less benignly, [[mosquito]]es are [[Disease vector|vectors]] for [[malaria]], [[dengue]], [[West Nile fever]], [[yellow fever]], [[encephalitis]], and other [[infectious diseases]]; and [[houseflies]], commensal with humans all over the world, spread [[foodborne illness]]es. Flies can be annoyances especially in some parts of the world where they can occur in large numbers, buzzing and settling on the skin or eyes to bite or seek fluids. Larger flies such as [[tsetse flies]] and [[screwworms]] cause significant economic harm to cattle. Blowfly larvae, known as [[Calliphoridae|gentles]], and other dipteran larvae, known more generally as [[maggot]]s, are used as [[fishing bait]], as food for carnivorous animals, and in medicine in [[debridement]], [[Maggot therapy|to clean wounds]].

== Taxonomy and phylogeny ==

=== Relationships to other insects ===

Dipterans are [[Holometabolism|holometabolous]], meaning that they undergo radical metamorphosis. They belong to the [[Mecopterida]], alongside the [[Mecoptera]], [[Siphonaptera]], [[Lepidoptera]] and [[Trichoptera]].<ref>{{cite journal |doi=10.1186/1471-2148-14-52 |pmid=24646345 |pmc=4000048 |title=The evolutionary history of holometabolous insects inferred from transcriptome-based phylogeny and comprehensive morphological data |journal=[[BMC Evolutionary Biology]] |volume=14 |issue=1 |page=52 |year=2014 |last1=Peters |first1=Ralph S. |last2=Meusemann |first2=Karen |last3=Petersen |first3=Malte |last4=Mayer |first4=Christoph |last5=Wilbrandt |first5=Jeanne |last6=Ziesmann |first6=Tanja |last7=Donath |first7=Alexander |last8=Kjer |first8=Karl M. |last9=Aspöck |first9=Ulrike |last10=Aspöck |first10=Horst |last11=Aberer |first11=Andre |last12=Stamatakis |first12=Alexandros |last13=Friedrich |first13=Frank |last14=Hünefeld |first14=Frank |last15=Niehuis |first15=Oliver |last16=Beutel |first16=Rolf G. |last17=Misof |first17=Bernhard |display-authors=6 |bibcode=2014BMCEE..14...52P |doi-access=free }}</ref><ref>{{cite web |url=http://www.taxonomy.nl/Taxonomicon/TaxonTree.aspx?id=102510 |title=Taxon: Superorder Antliophora |website=The Taxonomicon |access-date=21 August 2007}}</ref> The possession of a single pair of wings distinguishes most true flies from other insects with "fly" in their names. However, some true flies such as [[Hippoboscidae]] (louse flies) have become secondarily wingless.<ref>{{cite book |last=Hutson |first=A. M. |year=1984 |title=Diptera: Keds, flat-flies & bat-flies (Hippoboscidae & Nycteribiidae) |page=84 |publisher=[[Royal Entomological Society of London]] |series=[[Handbooks for the Identification of British Insects]] |volume=10 pt 7}}</ref><ref name="Mayhew 2007">{{cite journal |last=Mayhew |first=Peter J. |title=Why are there so many insect species? Perspectives from fossils and phylogenies |journal=[[Biological Reviews]] |volume=82 |issue=3 |year=2007 |pages=425–454 |doi=10.1111/j.1469-185X.2007.00018.x |pmid=17624962|s2cid=9356614 }}</ref>

The [[cladogram]] represents the current consensus view.<ref name=Kjer>{{Cite journal |last1=Kjer |first1=Karl M. |last2=Simon |first2=Chris|author2-link=Chris Simon (biologist) |last3=Yavorskaya |first3=Margarita |last4=Beutel |first4=Rolf G. |date=2016 |title=Progress, pitfalls and parallel universes: a history of insect phylogenetics |journal=[[Journal of the Royal Society Interface]] |volume=13 |issue=121 |page=121 |doi=10.1098/rsif.2016.0363 |pmid=27558853 |name-list-style=amp |pmc=5014063 }}</ref>

{{clade
|label1=[[Holometabola]]
|1={{clade
   |1=[[Hymenoptera]] (sawflies, wasps, ants, bees) [[File:European wasp white bg.jpg|70px]]
   |label2=[[Aparaglossata]]
   |2={{clade
      |label1=[[Neuropteroidea]]      
      |1={{clade
         |label1=[[Neuropterida]]
         |1={{clade
            |1=[[Raphidioptera]] (snakeflies) [[File:Raphidia icon.png|70px]]
            |label2=
            |2={{clade
               |1=[[Megaloptera]] (alderflies and allies) [[File:Corydalus cornutus illustration (rotated).png|70px]]
               |2=[[Neuroptera]] (Lacewings and allies) [[File:Osmylus_(white_background).jpg|70px]]
               }}
            }}
         |label2=[[Coleopterida]]
         |2={{clade
            |1=[[Coleoptera]] (beetles) [[File:Pseudacrossus przewalskyi (Reitter, 1887).jpg|50px]]
            |2=[[Strepsiptera]] (twisted-wing parasites) [[File:Elenchus koebelei.jpg|70px]]
            }}
         }}
      |label2=[[Panorpida]]|sublabel2=(Mecopterida)
      |2={{clade
         |label1=[[Amphiesmenoptera]]
         |1={{clade
            |1=[[Trichoptera]] (caddisflies) [[File:RHYACOPHILA DORSALIS Male Pont Forge de Sailly Watigny 02 MHNT.jpg|70px]] 
            |2=[[Lepidoptera]] (butterflies, moths) [[File:Arctia villica SLU.JPG|70px]]
            }}
         |label2=Antliophora
         |2={{clade 
            |1='''Diptera''' [[File:Common house fly, Musca domestica.jpg|70px]] 
            |2={{clade
               |1=[[Mecoptera]] (scorpionflies)  [[File:Scorpionfly (white background).jpg|70px]]
               |2=[[Siphonaptera]] (fleas) [[File:Pulex irritans female ZSM (white background).jpg|40px]]
               }}
            }}
         }}
      }}
   }}
}}

=== Relationships between subgroups and families ===

[[File:Fossil insect Diptera, Brachycera in Baltic amber. Age 50 Mill. years (the Lower Eocene).jpg|thumb|left|upright=0.7 |Fossil [[brachycera]]n in [[Baltic amber]]. [[Lower Eocene]], c. 50 million years ago]]

The first true dipterans known are from the [[Middle Triassic]] (around 240 million years ago), and they became widespread during the Middle and [[Late Triassic]].<ref>{{cite book |last1=Blagoderov |first1=V. A. |last2=Lukashevich |first2=E. D. |last3=Mostovski |first3=M. B. |editor1-last=Rasnitsyn |editor1-first=A. P. |editor2-last=Quicke |editor2-first=D. L. J. |year=2002 |title=History of Insects |chapter=Order Diptera Linné, 1758. The true flies |publisher=[[Kluwer Academic Publishers]] |isbn=978-1-4020-0026-3 |chapter-url=http://palaeoentomolog.ru/New/diptera.html}}</ref> [[Flowering plant|Modern flowering plants]] did not appear until the [[Cretaceous]] (around 140 million years ago), so the original dipterans must have had a different source of nutrition other than [[nectar]]. Based on the attraction of many modern fly groups to shiny droplets, it has been suggested that they may have fed on [[Honeydew (secretion)|honeydew]] produced by [[Homoptera|sap-sucking bugs]] which were abundant at the time, and dipteran mouthparts are well-adapted to softening and lapping up the crusted residues.<ref>{{cite journal |last1=Downes |first1=William L. Jr. |author2=Dahlem, Gregory A. |year=1987 |title= Keys to the Evolution of Diptera: Role of Homoptera |journal=[[Environmental Entomology]] |volume=16 |issue=4 |pages=847–854 |doi=10.1093/ee/16.4.847 }}</ref> The [[basal clade]]s in the Diptera include the [[Deuterophlebiidae]] and the enigmatic [[Nymphomyiidae]].<ref name="Wiegmann2011">{{cite journal |last1=Wiegmann |first1=B. M. |year=2011 |title=Episodic radiations in the fly tree of life |journal=[[PNAS]] |volume=108 |issue=14 |pages=5690–5695 |doi=10.1073/pnas.1012675108 |first2=M. D. |last3=Winkler |first3=I. S. |last4=Barr |first4=N. B. |last5=Kim |first5=J.-W. |last6=Lambkin |first6=C. |last7=Bertone |first7=M. A. |last8=Cassel |first8=B. K. |last9=Bayless |first9=K. M. |last10=Heimberg |first10=A. M. |last11=Wheeler |first11=B. M. |last12=Peterson |first12=K. J. |last13=Pape |first13=T. |last14=Sinclair |first14=B. J. |last15=Skevington |first15=J. H. |last16=Blagoderov |first16=V. |last17=Caravas |first17=J. |last18=Kutty |first18=S. N. |last19=Schmidt-Ott |first19=U. |last20=Kampmeier |first20=G. E. |last21=Thompson |first21=F. C. |last22=Grimaldi |first22=D. A. |last23=Beckenbach |first23=A. T. |last24=Courtney |first24=G. W. |last25=Friedrich |first25=M. |last26=Meier |first26=R. |last27=Yeates |first27=D. K. |pmid=21402926 |pmc=3078341 |display-authors=6 |last2=Trautwein |bibcode=2011PNAS..108.5690W |doi-access=free }}</ref> Three episodes of [[evolutionary radiation]] are thought to have occurred based on the fossil record. Many new species of lower Diptera developed in the [[Triassic]], about 220 million years ago. Many lower Brachycera appeared in the [[Jurassic]], some 180 million years ago. A third radiation took place among the [[Schizophora]] at the start of the [[Paleogene]], 66 million years ago.<ref name="Wiegmann2011" />

The [[Phylogenetic tree|phylogenetic]] position of Diptera has been controversial. The [[monophyly]] of [[holometabolous]] insects has long been accepted, with the main orders being established as Lepidoptera, Coleoptera, Hymenoptera and Diptera, and it is the relationships between these groups which has caused difficulties. Diptera is widely thought to be a member of [[Mecopterida]], along with Lepidoptera (butterflies and moths), Trichoptera (caddisflies), Siphonaptera (fleas), Mecoptera (scorpionflies) and possibly [[Strepsiptera]] (twisted-wing flies). Diptera has been grouped with Siphonaptera and Mecoptera in the Antliophora, but this has not been confirmed by molecular studies.<ref>{{cite book |last1=Wiegmann |first1=Brian |last2=Yeates |first2=David K. |title=The Evolutionary Biology of Flies |url=https://books.google.com/books?id=rElP5sNn6IYC |year=2012 |publisher=[[Columbia University Press]] |isbn=978-0-231-50170-5 |pages=4–6}}</ref>

[[File:Lutzomyia adiketis.jpg|thumb|right|upright=0.7 |Fossil [[nematocera]]n in Dominican amber. Sandfly, ''[[Lutzomyia adiketis]]'' ([[Psychodidae]]), [[Early Miocene]], c. 20 million years ago]]

Diptera were traditionally broken down into two suborders, [[Nematocera]] and [[Brachycera]], distinguished by the differences in antennae. The Nematocera are identified by their elongated bodies and many-segmented, often feathery antennae as represented by mosquitoes and crane flies. The Brachycera have rounder bodies and much shorter antennae.<ref>B.B. Rohdendorf. 1964. Trans. Inst. Paleont., Acad. Sci. USSR, Moscow, v. 100</ref><ref name=TOL>{{cite web |last1=Wiegmann |first1=Brian M. |last2=Yeates |first2=David K. |title=Diptera True Flies |url=http://tolweb.org/Diptera/8226 |website=Tree of Life |date=29 November 2007 |access-date=25 May 2016}}</ref> Subsequent studies have identified the Nematocera as being [[Paraphyly|paraphyletic]] with modern phylogenies placing the Brachycera within grades of groups formerly placed in the Nematocera. The construction of a phylogenetic tree has been the subject of ongoing research. The following cladogram is based on the FLYTREE project.<ref>{{cite web |last1=Yeates |first1=David K. |last2=Meier |first2=Rudolf |last3=Wiegmann |first3=Brian |title=Phylogeny of True Flies (Diptera): A 250 Million Year Old Success Story in Terrestrial Diversification |url=http://www.inhs.illinois.edu/research/flytree/flyphylogeny/ |website=Flytree |publisher=Illinois Natural History Survey |archive-url=https://web.archive.org/web/20151228210535/http://inhs.illinois.edu/research/flytree/flyphylogeny/ |archive-date=28 December 2015 |access-date=24 May 2016}}</ref><ref>{{cite journal |last1=Yeates |first1= David K. |last2=Weigmann |first2=Brian M |last3=Courtney |first3=Greg W. |last4=Meier |first4=Rudolf |last5=Lambkins |first5=Christine |last6=Pape |first6=Thomas |title=Phylogeny and systematics of Diptera: Two decades of progress and prospects |year=2007 |journal=[[Zootaxa]] |volume=1668 |pages=565–590 |doi=10.11646/zootaxa.1668.1.27 }}</ref>

{{clade | style=font-size:100%;line-height:105%;
 |label1='''Diptera'''
 |grouplabel1={{clade labels|label1="[[Nematocera]]" |top1=16%}}
 |1={{clade |bar1=green
  |1={{clade 
    |1=[[Ptychopteromorpha]] (phantom and primitive crane-flies) [[File:Ptychoptera contaminata male Walker 1856 plate-XXVIII.png|60px]]
    |2=[[Culicomorpha]] (mosquitoes, blackflies and midges) [[File:Stegomyia fasciata.jpg|55px]]
   }}
  |2={{clade
    |1=[[Blephariceromorpha]] (net-winged midges, etc) [[File:Imago of Blepharicera fasciata as Asthenia fasciata in Westwood 1842, plate 94.png|60px]]|bar1=green
    |2={{clade
     |1=[[Bibionomorpha]] (gnats) [[File:Isoneuromyia annandalei.jpg|55px]]|bar1=green
     |2={{clade
       |1=[[Psychodomorpha]] (drain flies, sand flies, etc) [[File:Clogmia_clean.jpg|55px]]|bar1=green
       |2={{clade
        |1=[[Tipulomorpha]] (crane flies) [[File:Tipula oleracea icon.jpg|65px]]|bar1=green
        |label2='''[[Brachycera]]'''
        |2={{clade
          |label1=
          |1={{clade
           |1=[[Stratiomyomorpha]] (soldier flies, etc) [[File:Hermetia illucens f.jpg|66px]]
           |2={{clade
             |1=[[Xylophagomorpha]] (stink flies, etc) [[File:Coenomyia_ferruginea.png|55px]]
             |2=[[Tabanomorpha]] (horse flies, snipe flies, etc) [[File:Chrysops relicta f.jpg|66px]]
            }}
           }}
          |label2=[[Muscomorpha|Mus]]
          |2={{clade
           |1=[[Nemestrinoidea]] [[File:Acrocera globulus.png|66px]]
           |2={{clade
             |1=[[Asiloidea]] (robber flies, bee flies, etc) [[File:Asilidae icon.jpg|66px]]
             |label2=[[Eremoneura|Ere]]
             |2={{clade
              |1=[[Empidoidea]] (dance flies, etc) [[File:Drapetis_brevior_fbi.jpg|35px]]
              |label2=[[Cyclorrhapha|Cyc]]
              |2={{clade
                |1=[[Aschiza]] (in part)
                |2={{clade
                 |1=[[Phoroidea]] (flat-footed flies, etc) [[File:Platypeza_picta.png|55px]]
                 |2={{clade
                   |1=[[Syrphoidea]] (hoverflies) [[File:Syrphidae icon.jpg|55px]]
                   |label2=[[Schizophora|Sch]]
                   |2={{clade
                    |label1=[[Calyptratae|Cal]]
                    |1={{clade
                      |1=[[Hippoboscoidea]] (louse flies, etc) [[File:Nycteribiidae icon.jpg|55px]]
                      |2={{clade
                       |1=[[Muscoidea]] (house flies, dung flies, etc) [[File:Musca_domestica_female.jpg|55px]]
                       |2=[[Oestroidea]] (blow flies, flesh flies, etc) [[File:Sarcophaga_haemorrhoidalis_m.jpg|55px]]
                       }}
                     }}
                    |2=[[Acalyptratae]] (marsh flies, fruit flies, etc) [[File:Ceratitis capitata illustration.jpg|55px]]
                    }}
                  }}
                 }}
               }}
              }}
            }}
           }}
         }}
        }}
      }}
     }}
   }}
  }}
}}

{{smalldiv|1=
''Abbreviations used in the cladogram:''
* Cal=[[Calyptratae]]
* Cyc=[[Cyclorrhapha]] 
* Ere=[[Eremoneura]] 
* Mus=[[Muscomorpha]]
* Sch=[[Schizophora]] 
}}

A 2023 study revised the phylogeny of the Nematocera. The grouping remains paraphyletic with respect to the Brachycera, but is rearranged, with [[Deuterophlebiidae]] basal (sister to the rest), [[Nymphomyiidae]] placed inside [[Culicomorpha]], and [[Blephariceridae]] within [[Psychodomorpha]]. Finally, [[Anisopodidae]] becomes sister to the Brachycera.<ref name="Zhang Yang 2023">{{cite journal |last1=Zhang |first1=Xiao |last2=Yang |first2=Ding |last3=Kang |first3=Zehui |title=New data on the mitochondrial genome of Nematocera (lower Diptera): features, structures and phylogenetic implications |journal=Zoological Journal of the Linnean Society |volume=197 |issue=1 |date=1 January 2023 |doi=10.1093/zoolinnean/zlac012 |pages=229–245 |url=https://academic.oup.com/zoolinnean/article/197/1/229/6554024|url-access=subscription }}</ref>

{{clade | style=font-size:100%;line-height:105%;
|label1='''Diptera'''
|grouplabel1={{clade labels |label1="[[Nematocera]]" |top1=40%}}
|1={{clade
   |1=[[Deuterophlebiidae]] |bar1=green
   |2={{clade 
      |1=[[Tipulomorpha]] (crane flies) [[File:Tipula oleracea icon.jpg|65px]] |bar1=green
      |2={{clade 
         |1=[[Axymyiomorpha]] [[File:Protaxymyia thuja (cropped).jpg|65px]] |bar1=green
         |2=[[Ptychopteromorpha]] (phantom and primitive crane-flies) [[File:Ptychoptera contaminata male Walker 1856 plate-XXVIII.png|60px]] |bar2=green
         |3=[[Culicomorpha]] (mosquitoes, blackflies and midges, inc. [[Nymphomyiidae]]) [[File:Stegomyia fasciata.jpg|55px]] |bar3=green
         |4={{clade 
            |1=[[Psychodomorpha]] (drain flies, sand flies, inc. [[Blephariceridae]]) [[File:Clogmia_clean.jpg|55px]]|bar1=green
            |2={{clade
               |1=[[Bibionomorpha]] (gnats) [[File:Isoneuromyia annandalei.jpg|55px]]|bar1=green
               |2={{clade
                  |1=[[Anisopodidae]] (wood gnats) [[File:Sylvicola fenestralis (cropped).jpg|60px]] |bar1=green
                  |2='''[[Brachycera]]'''
                  }}
               }}
            }} 
         }}
      }}
   }}
}}

===Diversity===

[[File:Mydas sp..JPG|thumb|''[[Gauromydas heros]]'' is the largest fly in the world.]]

Flies are often abundant and are found in almost all terrestrial habitats. They include many familiar insects such as house flies, blow flies, mosquitoes, gnats, black flies, midges and fruit flies. More than 150,000 have been [[Species description|formally described]] and the actual species diversity is much greater, with the flies from many parts of the world yet to be studied intensively.<ref name=Pape2009>{{cite book |last1=Pape |first1=Thomas |author2=Bickel, Daniel John |author3=Meier, Rudolf |title=Diptera Diversity: Status, Challenges and Tools |url=https://books.google.com/books?id=TqAeuBCVdjQC&pg=PR13 |year=2009 |publisher=[[Brill Publishers|Brill]] |isbn=978-90-04-14897-0 |page=13}}</ref><ref>{{Cite journal |title=Congruence and controversy: toward a higher-level phylogeny of diptera |journal=[[Annual Review of Entomology]] |volume=44 |pages=397–428 |last2=Wiegmann |first2=B. M. |date=1999 |doi=10.1146/annurev.ento.44.1.397 |pmid=15012378 |last1=Yeates |first1=D. K.}}</ref> The suborder Nematocera include generally small, slender insects with long antennae such as mosquitoes, gnats, midges and crane-flies, while the Brachycera includes broader, more robust flies with short antennae. Many nematoceran larvae are aquatic.<ref name=TolwebDiptera>{{cite web |url=http://tolweb.org/Diptera |title=Diptera: True flies |last1=Wiegmann |first1=Brian M. |last2=Yeates |first2=David K. |year=2007 |website=Tree of Life Web Project |access-date=27 May 2016}}</ref> There are estimated to be a total of about 19,000 species of Diptera in Europe, 22,000 in the Nearctic region, 20,000 in the Afrotropical region, 23,000 in the Oriental region and 19,000 in the Australasian region.<ref name=Pape>{{cite journal |last1=Pape |first1=Thomas |author2=Beuk, Paul |author3=Pont, Adrian Charles |author4=Shatalkin, Anatole I. |author5=Ozerov, Andrey L. |author6=Woźnica, Andrzej J. |author7=Merz, Bernhard |author8=Bystrowski, Cezary |author9=Raper, Chris |author10=Bergström, Christer |author11=Kehlmaier, Christian |author12=Clements, David K. |author13=Greathead, David |author14=Kameneva, Elena Petrovna |author15=Nartshuk, Emilia |author16=Petersen, Frederik T. |author17=Weber, Gisela |author18=Bächli, Gerhard |author19=Geller-Grimm, Fritz |author20=Van de Weyer, Guy |author21=Tschorsnig, Hans-Peter |author22=de Jong, Herman |author23=van Zuijlen, Jan-Willem |author24=Vaňhara, Jaromír |author25=Roháček, Jindřich |author26=Ziegler, Joachim |author27=Majer, József |author28=Hůrka, Karel |author29=Holston, Kevin |author30=Rognes, Knut |author31=Greve-Jensen, Lita |author32=Munari, Lorenzo |author33=de Meyer, Marc |author34=Pollet, Marc |author35=Speight, Martin C. D. |author36=Ebejer, Martin John |author37=Martinez, Michel |author38=Carles-Tolrá, Miguel |author39=Földvári, Mihály |author40=Chvála, Milan |author41=Barták, Miroslav |author42=Evenhuis, Neal L. |author43=Chandler, Peter J. |author44=Cerretti, Pierfilippo |author45=Meier, Rudolf |author46=Rozkosny, Rudolf |author47=Prescher, Sabine |author48=Gaimari, Stephen D. |author49=Zatwarnicki, Tadeusz |author50=Zeegers, Theo |author51=Dikow, Torsten |author52=Korneyev, Valery A. |author53=Richter, Vera Andreevna |author54=Michelsen, Verner |author55=Tanasijtshuk, Vitali N. |author56=Mathis, Wayne N. |author57=Hubenov, Zdravko |author58=de Jong, Yde |display-authors=5 |year=2015 |title=Fauna Europaea: Diptera – Brachycera |journal=[[Biodiversity Data Journal]] |volume=3 |issue=3 |pmc=4339814 |article-number=e4187 |doi=10.3897/BDJ.3.e4187 |pmid=25733962 |doi-access=free }}</ref> While most species have restricted distributions, a few like the housefly (''[[Musca domestica]]'') are cosmopolitan.<ref>{{Cite journal |last1=Marquez |first1=J. G. |last2=Krafsur |first2=E. S. |date=2002-07-01 |title=Gene Flow Among Geographically Diverse Housefly Populations (Musca domestica L.): A Worldwide Survey of Mitochondrial Diversity |url=https://zenodo.org/record/1059059 |journal=[[Journal of Heredity]]  |volume=93 |issue=4 |pages=254–259 |doi=10.1093/jhered/93.4.254 |pmid=12407211|doi-access=free }}</ref> ''[[Gauromydas heros]]'' ([[Asiloidea]]), with a length of up to {{convert |7 |cm |in |1 |abbr=on}}, is generally considered to be the largest fly in the world,<ref>{{cite news |title=World's Biggest Fly Faces Two New Challengers |last=Owen |first=James |url=http://news.nationalgeographic.com/2015/12/151210-biggest-animals-science-insects-flies-new-species/ |archive-url=https://web.archive.org/web/20151213125146/http://news.nationalgeographic.com/2015/12/151210-biggest-animals-science-insects-flies-new-species/ |archive-date=13 December 2015 |newspaper=National Geographic |date=10 December 2015 |access-date=21 July 2016}}</ref> while the smallest is ''[[Euryplatea nanaknihali]]'', which at {{convert |0.4 |mm |in |3 |abbr=on}} is smaller than a grain of salt.<ref>{{cite news |title=World's Tiniest Fly May Decapitate Ants, Live in Their Heads |last=Welsh |first=Jennifer |url=http://www.livescience.com/21326-smallest-fly-decapitates-ants.html |newspaper=Livescience |date=2 July 2012 |access-date=21 July 2016}}</ref>

Brachycera are ecologically very diverse, with many being predatory at the larval stage and some being parasitic. Animals parasitised include [[molluscs]], [[woodlice]], [[millipede]]s, insects, [[mammal]]s,<ref name=Pape/> and [[amphibian]]s.<ref>{{cite journal |last=Strijbosch |first=H. |year=1980 |title=Mortality in a population of ''Bufo bufo'' resulting from the fly ''Lucilia bufonivora'' |journal=[[Oecologia]] |volume=45 |issue=2 |pages=285–286 |doi=10.1007/BF00346472 |pmid=28309542 |bibcode=1980Oecol..45..285S |s2cid=32817424 }}</ref> Flies are the second largest group of pollinators after the Hymenoptera (bees, wasps and relatives). In wet and colder environments flies are significantly more important as pollinators. Compared to bees, they need less food as they do not need to provision their young. Many flowers that bear low nectar and those that have evolved [[Pollination trap|trap pollination]] depend on flies.<ref>{{Cite journal |last1=Ssymank |first1=Axel |last2=Kearns |first2=C. A. |last3=Pape |first3=Thomas |last4=Thompson |first4=F. Christian |date=2008-04-01 |title=Pollinating Flies (Diptera): A major contribution to plant diversity and agricultural production |journal=Biodiversity |volume=9 |issue=1–2 |pages=86–89 |doi=10.1080/14888386.2008.9712892|bibcode=2008Biodi...9a..86S |s2cid=39619017 }}</ref> It is thought that some of the earliest pollinators of plants may have been flies.<ref>{{Cite journal |last=Labandeira |first=Conrad C. |date=1998-04-03 |title=How Old Is the Flower and the Fly? |journal=[[Science (journal)|Science]] |volume=280 |issue=5360 |pages=57–59 |doi=10.1126/science.280.5360.57 |hdl=10088/5966 |s2cid=19305979 }}</ref>

The greatest diversity of gall-forming insects is found among the flies, principally among the gall midges ([[Cecidomyiidae]]).<ref>{{cite journal |doi=10.1016/j.baae.2005.07.002 |title=Adaptive radiation of gall-inducing insects |journal=Basic and Applied Ecology |volume=6 |issue=5 |pages=413–421 |year=2005 |last1=Price |first1=Peter W. |bibcode=2005BApEc...6..413P |doi-access=free }}</ref> Many flies (most importantly in the family Agromyzidae) lay their eggs in the mesophyll tissue of leaves with larvae feeding between the surfaces forming blisters and mines.<ref>{{cite journal |doi=10.1016/j.ympev.2006.12.018 |pmid=17291785 |title=Phylogenetic relationships within the leaf-mining flies (Diptera: Agromyzidae) inferred from sequence data from multiple genes |journal=[[Molecular Phylogenetics and Evolution]] |volume=42 |issue=3 |pages=756–75 |year=2007 |last1=Scheffer |first1=Sonja J. |last2=Winkler |first2=Isaac S. |last3=Wiegmann |first3=Brian M. |bibcode=2007MolPE..42..756S |url=https://zenodo.org/record/1259491 }}</ref> Some families feed on fungi. These include the cave dwelling fungus gnats ([[Mycetophilidae]]) whose larvae are bioluminescent, and the [[Sciaridae]]. Some plants are pollinated by fungus feeding flies that visit fungus-infected male flowers.<ref>{{Cite journal |last1=Sakai |first1=Shoko |last2=Kato |first2=Makoto |last3=Nagamasu |first3=Hidetoshi |date=2000 |title=Artocarpus (Moraceae)-Gall Midge Pollination Mutualism Mediated by a Male-Flower Parasitic Fungus |journal=[[American Journal of Botany]] |volume=87 |issue=3 |pages=440–445 |doi=10.2307/2656640|hdl=10088/12159 |jstor=2656640 |pmid=10719005 |bibcode=2000AmJB...87..440S |doi-access=free }}</ref>
 
The larvae of ''[[Megaselia scalaris]]'' (Phoridae) are omnivorous and may consume such substances as paint and shoe polish.<ref>{{cite journal |last=Disney |first=R.H.L. |year=2007 |title=Natural History of the Scuttle Fly, ''Megaselia scalaris'' |journal=[[Annual Review of Entomology]] |volume=53 |pages=39–60 |doi=10.1146/annurev.ento.53.103106.093415 |pmid=17622197 |url=https://tede.ufrrj.br/jspui/handle/jspui/1224 }}</ref> ''[[Exorista mella]]'' is a generalist and [[parasitoid]] of multiple hosts.<ref>{{Cite journal |last=Stireman |first=John O. |date=2002-09-01 |title=Learning in the Generalist Tachinid Parasitoid Exorista Mella Walker (Diptera: Tachinidae) |journal=[[Journal of Insect Behavior]] |volume=15 |issue=5 |pages=689–706 |doi=10.1023/A:1020752024329 |bibcode=2002JIBeh..15..689S |s2cid=36686371}}</ref> The larvae of shore flies ([[Ephydridae]]) and some [[Chironomidae|chironomid]] midges survive in extreme environments including glaciers (as in ''[[Diamesa]]'' sp.<ref name="Biology of Shore Flies">{{cite journal |last1=Foote |first1=B. A. |title=Biology of Shore Flies |journal=[[Annual Review of Entomology]] |volume=40 |pages=417–442 |year=1995 |doi=10.1146/annurev.en.40.010195.002221}}</ref>), hot springs, geysers, saline pools, sulphur pools, septic tanks and even crude oil (''[[Helaeomyia petrolei]]''<ref name="Biology of Shore Flies"/>).<ref name="Pape"/> Adult [[hoverflies]] (Syrphidae) are well known for their [[mimicry]] and the larvae adopt diverse lifestyles including being [[inquiline]] [[scavenger]]s inside the nests of social insects.<ref name="Gullan320">{{cite book |last1=Gullan |first1=P.J. |last2=Cranston |first2=P.S. |title=The Insects: An Outline of Entomology |url=https://books.google.com/books?id=E_6-pGOLUgcC&pg=PA320 |year=2009 |publisher=John Wiley & Sons |isbn=978-1-4051-4457-5 |page=320}}</ref> Some brachycerans are agricultural pests, some bite animals and humans and suck their blood, and some transmit diseases.<ref name="Pape"/>

== Anatomy and morphology ==

{{see also |Morphology of Diptera }}

Flies are adapted for aerial movement and typically have short and streamlined bodies. The first [[tagma (biology)|tagma]] of the fly, the head, bears the eyes, the [[antenna (biology)|antenna]]e, and the [[insect mouthparts|mouthparts]] (the labrum, labium, mandible, and maxilla make up the mouthparts). The second tagma, the [[Thorax (insect anatomy)|thorax]], bears the wings and contains the flight muscles on the second segment, which is greatly enlarged; the first and third segments have been reduced to collar-like structures, and the third segment bears the [[halteres]], which help to balance the insect during flight. The third tagma is the [[Abdomen#Arthropoda|abdomen]] consisting of 11 segments, some of which may be fused, and with the three hindmost segments modified for reproduction.<ref name="Dickinson 1999">{{Cite journal |last=Dickinson |first=Michael H. |date=1999 |title=Haltere–mediated equilibrium reflexes of the fruit fly, Drosophila melanogaster |journal=Philosophical Transactions of the Royal Society of London B: Biological Sciences |volume=354 |issue=1385 |pages=903–916 |doi=10.1098/rstb.1999.0442 |pmc=1692594 |pmid=10382224}}</ref><ref name=Resh/> Some Dipterans are mimics and can only be distinguished from their models by very careful inspection. An example of this is ''[[Spilomyia longicornis]]'', which is a fly but mimics a [[vespid]] wasp.<ref>{{cite work|author=Penney, H.|date=2001|title=Evolution of Imperfect Mimicry: Explaining Variation in Mimetic Fidelity among Syrphid Species|place= Ottawa, ON|publisher=Carleton University|url=https://curve.carleton.ca/system/files/etd/c3df345b-38ec-4006-8143-6698a6294f9d/etd_pdf/d4161934a9585fb98190d9a19bed4e1b/penney-evolutionofimperfectmimicryexplainingvariation.pdf|access-date=10 August 2025}}</ref>

[[File:Tabanus atratus, U, Face, MD 2013-08-21-16.06.31 ZS PMax (9599360121).jpg|thumb|left|Head of [[Tabanus atratus|a horse-fly]] showing large [[compound eye]]s and stout piercing [[insect mouthparts|mouthparts]] ]]
[[File:Tephrochlamys rufiventris (female head) (25234095874).jpg|thumb|left|Head of a fly, showing the two compound eyes and three simple eyes]]

Flies have a mobile head with a pair of large [[compound eye]]s on the sides of the head, and in most species, three small [[ocelli]] on the top. The compound eyes may be close together or widely separated, and in some instances are divided into a dorsal region and a ventral region, perhaps to assist in swarming behaviour. The antennae are well-developed but variable, being thread-like, feathery or comb-like in the different families. The mouthparts are adapted for piercing and sucking, as in the black flies, mosquitoes and robber flies, and for lapping and sucking as in many other groups.<ref name=Resh/> Female [[horse-flies]] use knife-like mandibles and maxillae to make a cross-shaped incision in the host's skin and then lap up the blood that flows. The gut includes large [[Diverticulum|diverticulae]], allowing the insect to store small quantities of liquid after a meal.<ref name="IIBD" />

For visual course control, flies' [[optic flow]] field is analyzed by a set of motion-sensitive neurons.<ref name=pmid11943823>{{cite journal |first1=Juergen |last1=Haag |first2=Alexander |last2=Borst |pmid=11943823 |pmc=6757520 |year=2002 |title=Dendro-dendritic interactions between motion-sensitive large-field neurons in the fly |volume=22 |issue=8 |pages=3227–3233 |journal=[[The Journal of Neuroscience]] |doi=10.1523/JNEUROSCI.22-08-03227.2002 }}</ref> A subset of these neurons is thought to be involved in using the optic flow to estimate the parameters of self-motion, such as yaw, roll, and sideward translation.<ref>{{cite book |doi=10.1007/978-3-642-74082-4_18 |chapter=Neural Mechanisms of Visual Course Control in Insects |title=Facets of Vision |year=1989 |last1=Hausen |first1=Klaus |last2=Egelhaaf |first2=Martin |isbn=978-3-642-74084-8 |pages=391–424 |editor1-first=Doekele Gerben |editor1-last=Stavenga |editor2-first=Roger Clayton |editor2-last=Hardie|chapter-url=https://pub.uni-bielefeld.de/record/1774636 }}</ref> Other neurons are thought to be involved in analyzing the content of the visual scene itself, such as separating figures from the ground using motion parallax.<ref>{{cite journal |first1=Martin |last1=Egelhaaf |year=1985 |title=On the neuronal basis of figure-ground discrimination by relative motion in the visual system of the fly |journal=Biological Cybernetics |volume=52 |issue=3 |pages=195–209 |url=https://link.springer.com/article/10.1007%2FBF00339948 |doi=10.1007/BF00339948 |s2cid=227306897 |url-access=subscription }}</ref><ref>{{cite journal |first1=Bernd |last1=Kimmerle |first2=Martin |last2=Egelhaaf |pmid=10934276 |pmc=6772600 |year=2000 |title=Performance of fly visual interneurons during object fixation |volume=20 |issue=16 |pages=6256–66 |journal=[[The Journal of Neuroscience]] |doi=10.1523/JNEUROSCI.20-16-06256.2000 }}</ref> The [[H1 neuron]] is responsible for detecting horizontal motion across the entire visual field of the fly, allowing the fly to generate and guide stabilizing motor corrections midflight with respect to yaw.<ref name="DoiBFMissing">{{cite journal |doi=10.1007/BF00660179 |title=Functional properties of the H1-neurone in the third optic Ganglion of the Blowfly, ''Phaenicia'' |year=1980 |last1=Eckert |first1=Hendrik |journal=[[Journal of Comparative Physiology]] |volume=135 |issue=1 |pages=29–39|s2cid=26541123 }}</ref> The ocelli are concerned in the detection of changes in light intensity, enabling the fly to react swiftly to the approach of an object.<ref name=Ruppert>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |pages=735–736 }}</ref>

Like other insects, flies have [[chemoreceptor]]s that detect smell and taste, and [[mechanoreceptor]]s that respond to touch. The third segments of the antennae and the maxillary palps bear the main olfactory receptors, while the gustatory receptors are in the labium, pharynx, feet, wing margins and female genitalia,<ref>{{cite journal |last=Stocker |first=Reinhard F. |year=2005 |title=The organization of the chemosensory system in ''Drosophila melanogaster'': a review |journal=Cell and Tissue Research |volume=275 |issue=1 |pages=3–26 |doi=10.1007/BF00305372|pmid=8118845 |s2cid=23210046 }}</ref> enabling flies to taste their food by walking on it. The taste receptors in females at the tip of the abdomen receive information on the suitability of a site for ovipositing.<ref name=Ruppert/> Flies that feed on blood have special sensory structures that can detect [[infrared]] emissions, and use them to home in on their hosts. Many blood-sucking flies can detect the raised concentration of [[carbon dioxide]] that occurs near large animals.<ref>{{cite journal |last1=Zhu |first1=Junwei J. |last2=Zhang |first2=Qing-he |last3=Taylor |first3=David B. |last4=Friesen |first4=Kristina A. |date=2016-09-01 |title=Visual and olfactory enhancement of stable fly trapping |url=http://digitalcommons.unl.edu/usdaarsfacpub/1555 |journal=Pest Management Science |volume=72 |issue=9 |pages=1765–1771 |doi=10.1002/ps.4207|pmid=26662853 |bibcode=2016PMSci..72.1765Z }}</ref> Some tachinid flies (Ormiinae) which are parasitoids of [[Tettigoniidae|bush crickets]], have sound receptors to help them locate their singing hosts.<ref>{{cite journal |last1=Lakes-Harlan |first1=Reinhard |author2=Jacobs, Kirsten |author3=Allen, Geoff R. |year=2007 |title=Comparison of auditory sense organs in parasitoid Tachinidae (Diptera) hosted by Tettigoniidae (Orthoptera) and homologous structures in a non-hearing Phoridae (Diptera) |journal=Zoomorphology |volume=126 |issue=4 |pages=229–243 |doi=10.1007/s00435-007-0043-3 |s2cid=46359462 }}</ref>

[[File:Halteres-Tipule.jpg|thumb|A [[crane fly]], showing the hind wings reduced to drumstick-shaped [[haltere]]s]]

Diptera have one pair of fore [[insect wing|wings]] on the [[mesothorax]] and a pair of [[halteres]], or reduced hind wings, on the [[metathorax]]. A further adaptation for flight is the reduction in number of the neural [[ganglia]], and concentration of nerve tissue in the thorax, a feature that is most extreme in the highly derived Muscomorpha infraorder.<ref name=IIBD>{{cite book |last1=Hoell |first1=H. V. |last2=Doyen |first2=J. T. |last3=Purcell |first3=A. H. |year=1998 |title=Introduction to Insect Biology and Diversity |edition=2nd |publisher= Oxford University Press |isbn=978-0-19-510033-4 |pages=493–499}}</ref> Some flies such as the ectoparasitic [[Nycteribiidae]] and [[Streblidae]] are exceptional in having lost their wings and become flightless. The only other order of insects bearing a single pair of true, functional wings, in addition to any form of halteres, are the [[Strepsiptera]]. In contrast to the flies, the Strepsiptera bear their halteres on the mesothorax and their flight wings on the metathorax.<ref>{{cite web |url=http://www.ento.csiro.au/education/insects/strepsiptera.html |title=Strepsiptera: ''Stylops'' |website=Insects and their Allies |publisher=[[CSIRO]] |access-date=25 May 2016}}</ref> Each of the fly's six [[Arthropod leg|legs]] has a typical insect structure of coxa, trochanter, femur, tibia and tarsus, with the tarsus in most instances being subdivided into five [[tarsomere]]s.<ref name=Resh/> At the tip of the limb is a pair of claws, and between these are cushion-like structures known as [[pulvilli]] which provide adhesion.<ref>{{cite journal |last1=Langer |first1=Mattias G. |last2=Ruppersberg |first2=J. Peter |last3=Gorb |first3=Stanislav N. |year=2004 |title=Adhesion Forces Measured at the Level of a Terminal Plate of the Fly's Seta |journal=Proceedings of the Royal Society B |volume=271 |issue=1554 |pages=2209–2215 |jstor=4142949 |doi=10.1098/rspb.2004.2850 |pmid=15539345 |pmc=1691860}}</ref>

The abdomen shows considerable variability among members of the order. It consists of eleven segments in primitive groups and ten segments in more derived groups, the tenth and eleventh segments having fused.<ref name=Gibb>{{cite book |last1=Gibb |first1=Timothy J. |last2=Oseto |first2=Christian |title=Arthropod Collection and Identification: Laboratory and Field Techniques |url=https://books.google.com/books?id=kyZGPWmILq0C&pg=PA189 |year=2010 |publisher=Academic Press |isbn=978-0-08-091925-6 |page=189}}</ref> The last two or three segments are adapted for reproduction. Each segment is made up of a dorsal and a ventral [[sclerite]], connected by an elastic membrane. In some females, the sclerites are rolled into a flexible, telescopic [[ovipositor]].<ref name=Resh/>

===Flight===

{{Further|Insect flight}}

[[File:March-fly-in-flight.jpg|thumb|A [[Horse-fly|tabanid]] in [[Insect flight|flight]] ]]

Flies are capable of great manoeuvrability during flight due to the presence of the halteres. These act as [[gyroscopic]] organs and are rapidly oscillated in time with the wings; they act as a balance and guidance system by providing rapid feedback to the wing-steering muscles, and flies deprived of their halteres are unable to fly. The wings and halteres move in synchrony but the amplitude of each wing beat is independent, allowing the fly to turn sideways.<ref name="Sane 2015">{{cite journal |last1=Deora |first1=Tanvi |last2=Singh |first2=Amit Kumar |last3=Sane |first3=Sanjay P. |title=Biomechanical basis of wing and haltere coordination in flies |journal=[[PNAS]] |date=3 February 2015 |volume=112 |issue=5 |pages=1481–1486 |doi=10.1073/pnas.1412279112 |pmid=25605915 |pmc=4321282|bibcode=2015PNAS..112.1481D |doi-access=free }}</ref> The wings of the fly are attached to two kinds of muscles, those used to power it and another set used for fine control.<ref>{{Cite journal |last1=Dickinson |first1=Michael H |last2=Tu |first2=Michael S |date=1997-03-01 |title=The function of dipteran flight muscle |journal=Comparative Biochemistry and Physiology Part A: Physiology |volume=116 |issue=3 |pages=223–238 |doi=10.1016/S0300-9629(96)00162-4}}</ref>

Flies tend to fly in a straight line then make a rapid change in direction before continuing on a different straight path. The directional changes are called [[saccade]]s and typically involve an angle of 90°, being achieved in 50 milliseconds. They are initiated by visual stimuli as the fly observes an object, nerves then activate steering muscles in the thorax that cause a small change in wing stroke which generate sufficient torque to turn. Detecting this within four or five wingbeats, the halteres trigger a counter-turn and the fly heads off in a new direction.<ref>{{cite journal |last=Dickinson |first=Michael H. |year=2005 |title=The initiation and control of rapid flight manoeuvres in fruit flies |journal=Integrative and Comparative Biology |volume=45 |issue=2 |pages=274–281 |doi=10.1093/icb/45.2.274 |pmid=21676771 |s2cid=7306151 |doi-access=free }}</ref>

Flies have rapid reflexes that aid their escape from predators but their sustained flight speeds are low. [[Dolichopus pennatus|Dolichopodid]] flies in the genus ''Condylostylus'' respond in less than five milliseconds to camera flashes by taking flight.<ref>{{cite journal |doi=10.1653/024.094.0240 |title=Faster than a flash: The fastest visual startle reflex response is found in a long-legged fly, ''Condylostylus'' sp. (Dolichopodidae) |journal=[[The Florida Entomologist]] |volume=94 |issue=2 |pages=367–369 |year=2011 |last1=Sourakov |first1=Andrei|s2cid=86502767 |doi-access=free }}</ref> In the past, the deer bot fly, ''[[Cephenemyia]]'', was claimed to be one of the fastest insects on the basis of an estimate made visually by [[Charles Henry Tyler Townsend|Charles Townsend]] in 1927.<ref>{{cite journal |title=On the ''Cephenemyia'' mechanism and the Daylight-Day circuit of the Earth by flight |last=Townsend |first=Charles H.T. |journal=Journal of the New York Entomological Society |volume=35 |issue=3 |year=1927 |pages=245–252 |jstor=25004207}}</ref> This claim, of speeds of 600 to 800 miles per hour, was regularly repeated until it was shown to be physically impossible as well as incorrect by Irving Langmuir. Langmuir suggested an estimated speed of 25 miles per hour.<ref>{{cite journal |journal=Science |volume=87 |issue=2254 |pages=233–234 |year=1938 |last=Langmuir |first=Irving |title=The speed of the deer fly |pmid=17770404 | doi=10.1126/science.87.2254.233| bibcode=1938Sci....87..233L }}</ref><ref>{{cite journal |title=Speed of ''Cephenemyia'' |last=Townsend |first=Charles H.T. |journal=Journal of the New York Entomological Society |volume=47 |issue=1 |year=1939 | pages=43–46 |jstor=25004791}}</ref><ref>{{cite journal |doi=10.1093/ae/45.1.4 |title=Getting Up to Speed |journal=American Entomologist |volume=45 |pages=4–5 |year=1999 |last1=Berenbaum |first1=M.|doi-access=free }}</ref>

Although most flies live and fly close to the ground, a few are known to fly at heights and a few like ''Oscinella'' (Chloropidae) are known to be dispersed by winds at altitudes of up to 2,000&nbsp;ft and over long distances.<ref>{{cite journal |title=High altitude migration of ''Oscinella frit'' L. (Diptera: Chloropidae) |last1=Johnson |first1=C.G. |author2=Taylor, L.R. |author3=T.R.E. Southwood |journal=Journal of Animal Ecology |volume=31 |issue=2 |year=1962 |pages=373–383 |jstor=2148 |doi=10.2307/2148 |bibcode=1962JAnEc..31..373J }}</ref> Some hover flies like ''Metasyrphus corollae'' have been known to undertake long flights in response to aphid population spurts.<ref>{{cite journal |doi=10.1111/j.1365-2311.1984.tb00856.x |title=Why does the hoverfly ''Metasyrphus corollae'' migrate? |journal=Ecological Entomology |volume=9 |issue=3 |pages=329–335 |year=1984 |last1=Svensson |first1=BO G. |last2=Janzon |first2=Lars-ÅKE|bibcode=1984EcoEn...9..329S |s2cid=83629356 }}</ref>

Males of fly species such as ''[[Cuterebra]]'', many hover flies,<ref>{{cite journal |doi=10.4039/Ent113695-8 |title=Territoriality in the Drone Fly, ''Eristalis tenax'' (Diptera: Syrphidae) |journal=The Canadian Entomologist |volume=113 |issue=8 |pages=695–704 |year=2012 |last1=Wellington |first1=W. G. |last2=Fitzpatrick |first2=Sheila M.|s2cid=86181761 }}</ref> bee flies (Bombyliidae)<ref>{{cite journal |doi=10.1007/BF01052332 |title=The mating system of a bee fly (Diptera: Bombyliidae). II. Factors affecting male territorial and mating success |journal=Journal of Insect Behavior |volume=3 |issue=5 |pages=619–636 |year=1990 |last1=Dodson |first1=Gary |last2=Yeates |first2=David|bibcode=1990JIBeh...3..619D |s2cid=25061334 }}</ref> and fruit flies (Tephritidae)<ref name="ReferenceA">{{cite journal |doi=10.1163/156853909X410766 |title=Territorial contests within and between two species of flies (Diptera: Richardiidae) in the wild |journal=Behaviour |volume=146 |issue=2 |pages=245–262 |year=2009 |last1=Becerril-Morales |first1=Felipe |last2=Macías-Ordóñez |first2=Rogelio}}</ref> maintain territories within which they engage in aerial pursuit to drive away intruding males and other species.<ref>{{cite journal |doi=10.1016/S0003-3472(83)80074-8 |title=Hilltop territoriality in a Sonoran desert bot fly (Diptera: Cuterebridae) |journal=Animal Behaviour |volume=31 |issue=2 |page=518 |year=1983 |last1=Alcock |first1=John |last2=Schaefer |first2=John E.|s2cid=53180240 }}</ref> While these territories may be held by individual males, some species, such as ''[[Anopheles freeborni|A. freeborni]]'',<ref>{{Cite journal |last1=Yuval |first1=B. |last2=Bouskila |first2=A. |date=1993-03-01 |title=Temporal dynamics of mating and predation in mosquito swarms|journal=Oecologia |volume=95 |issue=1 |pages=65–69 |doi=10.1007/BF00649508 |pmid=28313313|bibcode=1993Oecol..95...65Y |s2cid=22921039}}</ref> form [[lek mating|leks]] with many males aggregating in displays.<ref name="ReferenceA"/> Some flies maintain an airspace and still others form dense swarms that maintain a stationary location with respect to landmarks. Many flies mate in flight while swarming.<ref>{{cite journal |doi=10.1146/annurev.en.14.010169.001415 |title=The swarming and mating flight of Diptera |journal=Annual Review of Entomology |volume=14 |pages=271–298 |year=1969 |last1=Downes |first1=J. A.}}</ref>

== Life cycle and development ==

{{see also |Biology of Diptera}}

[[File:Anthomyiidae sp. 1 (aka).jpg|thumb|Mating [[Anthomyiidae|anthomyiid flies]]]]

Diptera go through a complete metamorphosis with four distinct life stages – egg, larva, pupa and adult.

=== Larva ===

In many flies, the larval stage is long and adults may have a short life. Most dipteran larvae develop in protected environments; many are aquatic and others are found in moist places such as carrion, fruit, vegetable matter, fungi and, in the case of parasitic species, inside their hosts. They tend to have thin cuticles and become desiccated if exposed to the air. Apart from the [[Brachycera]], most dipteran larvae have sclerotised head capsules, which may be reduced to remnant mouth hooks; the Brachycera, however, have soft, gelatinized head capsules from which the sclerites are reduced or missing. Many of these larvae retract their heads into their thorax.<ref name=Resh/><ref name=Gullan/> The [[Spiracle (arthropods)|spiracles]] in the larva and pupa do not have any internal mechanical closing device.<ref>[https://esc-sec.ca/wp/wp-content/uploads/2017/03/AAFC_manual_of_nearctic_diptera_vol_1.pdf Manual of Nearctic Diptera]</ref>

[[File:Stomoxys-stable-fly-life-cycle-2.jpg|thumb|left|Life cycle of stable fly ''[[Stomoxys calcitrans]]'', showing eggs, 3 [[larva]]l [[instar]]s, [[pupa]], and adult]]

Some other anatomical distinction exists between the larvae of the [[Nematocera]] and the [[Brachycera]]. Especially in the Brachycera, little demarcation is seen between the thorax and abdomen, though the demarcation may be visible in many Nematocera, such as mosquitoes; in the Brachycera, the head of the larva is not clearly distinguishable from the rest of the body, and few, if any, sclerites are present. Informally, such brachyceran larvae are called maggots,<ref name="isbn0-19-861271-0">{{cite book |last=Brown |first=Lesley |title=The New shorter Oxford English dictionary on historical principles |publisher=Clarendon |year=1993 |isbn=978-0-19-861271-1 |url-access=registration |url=https://archive.org/details/newshorteroxford00lesl }}</ref> but the term is not technical and often applied indifferently to fly larvae or insect larvae in general. The eyes and antennae of brachyceran larvae are reduced or absent, and the abdomen also lacks appendages such as [[cercus|cerci]]. This lack of features is an adaptation to food such as carrion, decaying detritus, or host tissues surrounding [[endoparasites]].<ref name="IIBD" /> Nematoceran larvae generally have well-developed eyes and antennae, while those of Brachyceran larvae are reduced or modified.<ref name=Lancaster>{{cite book |last1=Lancaster |first1=Jill |last2=Downes |first2=Barbara J. |title=Aquatic Entomology |url=https://books.google.com/books?id=jNAUDAAAQBAJ&pg=PA16 |year=2013 |publisher=Oxford University Press |isbn=978-0-19-957321-9 |page=16}}</ref>

Dipteran larvae have no jointed, "true legs",<ref name=Gullan>{{cite book |last1=Gullan |first1=P.J. |last2=Cranston |first2=P.S. |title=The Insects: An Outline of Entomology 3rd Edition |publisher=John Wiley & Sons |isbn=978-1-4051-4457-5 |year = 2005 |pages = 499–505}}</ref> but some dipteran larvae, such as species of [[Simuliidae]], [[Tabanidae]] and [[Vermileonidae]], have [[proleg]]s adapted to hold onto a substrate in flowing water, host tissues or prey.<ref>{{cite book |last=Chapman |first=R. F. |title=The Insects; Structure & Function |url=https://archive.org/details/insectsstructure0000chap |url-access=registration |year=1998 |publisher=Cambridge University Press |location=Cambridge |isbn=978-0-521-57890-5}}</ref> The majority of dipterans are [[oviparous]] and lay batches of eggs, but some species are [[ovoviviparous]], where the larvae starting development inside the eggs before they hatch or viviparous, the larvae hatching and maturing in the body of the mother before being externally deposited. These are found especially in groups that have larvae dependent on food sources that are short-lived or are accessible for brief periods.<ref>{{Cite journal |last1=Meier |first1=Rudolf |last2=Kotrba |first2=Marion |last3=Ferrar |first3=Paul |date=August 1999 |title=Ovoviviparity and viviparity in the Diptera |journal=Biological Reviews |volume=74 |issue=3 |pages=199–258 |doi=10.1111/j.1469-185X.1999.tb00186.x|s2cid=86129322 }}</ref> This is widespread in some families such as the Sarcophagidae. In ''[[Hylemya strigosa]]'' (Anthomyiidae) the larva moults to the second instar before hatching, and in ''[[Termitoxenia]]'' (Phoridae) females have incubation pouches, and a full developed third instar larva is deposited by the adult and it almost immediately pupates with no freely feeding larval stage. The [[tsetse fly]] (as well as other Glossinidae, Hippoboscidae, Nycteribidae and Streblidae) exhibits [[adenotrophic viviparity]]; a single fertilised egg is retained in the oviduct and the developing larva feeds on glandular secretions. When fully grown, the female finds a spot with soft soil and the larva works its way out of the oviduct, buries itself and pupates. Some flies like ''[[Lundstroemia parthenogenetica]]'' (Chironomidae) reproduce by [[thelytokous]] [[parthenogenesis]], and some [[gall midge]]s have larvae that can produce eggs ([[paedogenesis]]).<ref>{{Cite journal |last1=Mcmahon |first1=Dino P. |last2=Hayward |first2=Alexander |date=April 2016 |title=Why grow up? A perspective on insect strategies to avoid metamorphosis |journal=Ecological Entomology |volume=41 |issue=5 |pages=505–515 |doi=10.1111/een.12313|bibcode=2016EcoEn..41..505M |s2cid=86908583 |doi-access=free }}</ref><ref>{{cite book |title=Entomology |last=Gillott |first=Cedric |publisher=Springer |year=2005 |edition=3|pages=614–615}}</ref>

=== Pupa ===

The [[pupa]]e take various forms. In some groups, particularly the Nematocera, the pupa is intermediate between the larval and adult form; these pupae are described as "obtect", having the future appendages visible as structures that adhere to the pupal body. The outer surface of the pupa may be leathery and bear spines, respiratory features or locomotory paddles. In other groups, described as "coarctate", the appendages are not visible. In these, the outer surface is a [[puparium]], formed from the last larval skin, and the actual pupa is concealed within. When the adult insect is ready to emerge from this tough, desiccation-resistant capsule, it inflates [[ptilinum|a balloon-like structure on its head]], and forces its way out.<ref name=Resh/>

=== Adult ===

The adult stage is usually short, its function is only to mate and lay eggs. The genitalia of male flies are rotated to a varying degree from the position found in other insects.<ref>{{Cite web |url=http://psyche.entclub.org/48/48-079.html |title=Crampton, G. The TemporalAbdominal Structures of Male Diptera. |access-date=22 May 2018 |archive-date=23 May 2018 |archive-url=https://web.archive.org/web/20180523095550/http://psyche.entclub.org/48/48-079.html }}</ref> In some flies, this is a temporary rotation during mating, but in others, it is a permanent torsion of the organs that occurs during the pupal stage. This torsion may lead to the [[anus]] being below the genitals, or, in the case of 360° torsion, to the sperm duct being wrapped around the gut and the external organs being in their usual position. When flies mate, the male initially flies on top of the female, facing in the same direction, but then turns around to face in the opposite direction. This forces the male to lie on his back for his genitalia to remain engaged with those of the female, or the torsion of the male genitals allows the male to mate while remaining upright. This leads to flies having more reproduction abilities than most insects, and much quicker. Flies occur in large populations due to their ability to mate effectively and quickly during the mating season.<ref name="IIBD" /> More primitive groups mates in the air during swarming, but most of the more advanced species with a 360° torsion mate on a substrate.<ref>[https://web.archive.org/web/20160413002209/https://www.newscientist.com/article/mg12717314-500-sex-with-a-twist-in-the-tail-the-common-or-garden-housefly/ Sex with a twist in the tail: The common-or-garden housefly]</ref>

== Ecology ==

=== Trophic levels ===

[[File:Bubbling Fly.jpg|left|thumb|A calliphorid "bubbling"]]

As ubiquitous insects, dipterans play an important role at various [[trophic level]]s both as consumers and as prey. In some groups the larvae complete their development without feeding, and in others the adults do not feed. The larvae can be herbivores, scavengers, decomposers, predators or parasites, with the consumption of decaying organic matter being one of the most prevalent feeding behaviours. The fruit or detritus is consumed along with the associated micro-organisms, a sieve-like filter in the pharynx being used to concentrate the particles, while flesh-eating larvae have mouth-hooks to help shred their food. The larvae of some groups feed on or in the living tissues of plants and fungi, and some of these are serious pests of agricultural crops. Some aquatic larvae consume the films of algae that form underwater on rocks and plants. Many of the parasitoid larvae grow inside and eventually kill other arthropods, while parasitic larvae may attack vertebrate hosts.<ref name=Resh/>

=== Habitats and ecological niches ===

Whereas many dipteran larvae are aquatic or live in enclosed terrestrial locations, the majority of adults live above ground and are capable of flight. Predominantly they feed on nectar or plant or animal exudates, such as honeydew, for which their lapping mouthparts are adapted. Some flies have functional mandibles that may be used for biting. The flies that feed on vertebrate blood have sharp stylets that pierce the skin, with some species having anticoagulant saliva that is regurgitated before absorbing the blood that flows; in this process, certain diseases can be transmitted. The bot flies (Oestridae) have evolved to parasitize mammals. Many species complete their life cycle inside the bodies of their hosts.<ref>{{Cite book |title=The World Oestridae (Diptera), Mammals and Continental Drift  |last=Papavero |first=N. |publisher=Springer |year=1977 |isbn= 978-94-010-1308-6|doi=10.1007/978-94-010-1306-2|s2cid=43307061 }}</ref> The larvae of a few fly groups (Agromyzidae, Anthomyiidae, Cecidomyiidae) are capable of inducing plant galls. Some dipteran larvae are leaf-miners. The larvae of many brachyceran families are predaceous. In many dipteran groups, swarming is a feature of adult life, with clouds of insects gathering in certain locations; these insects are mostly males, and the swarm may serve the purpose of making their location more visible to females.<ref name="Resh" />

Most adult diptera have their mouthparts modified to sponge up fluid. The adults of many species of flies (e.g. ''[[Anthomyia]]'' sp., ''[[Steganopsis melanogaster]]'') that feed on liquid food will [[Regurgitation (digestion)|regurgitate]] fluid in a behaviour termed as "bubbling" which has been thought to help the insects evaporate water and concentrate food<ref>{{Cite journal |last1=Hendrichs |first1=J. |last2=Cooley |first2=S. S. |last3=Prokopy |first3=R. J.|date=1992 |title=Post-feeding bubbling behaviour in fluid-feeding Diptera: concentration of crop contents by oral evaporation of excess water |journal=Physiological Entomology |volume=17 |issue=2 |pages=153–161 |doi=10.1111/j.1365-3032.1992.tb01193.x |s2cid=86705683}}</ref> or possibly to cool by evaporation.<ref>{{Cite journal |last1=Gomes |first1=Guilherme |last2=Köberle |first2=Roland |last3=Von Zuben |first3=Claudio J. |last4=Andrade |first4=Denis V. |date=2018 |title=Droplet bubbling evaporatively cools a blowfly |journal=Scientific Reports |volume=8|issue=1 |page=5464 |doi=10.1038/s41598-018-23670-2 |pmc=5908842 |pmid=29674725 |bibcode=2018NatSR...8.5464G}}</ref> Some adult diptera are known for [[kleptoparasitism]] such as members of the Sarcophagidae. The miltogramminae are known as "satellite flies" for their habit of following wasps and stealing their stung prey or laying their eggs into them. Phorids, milichids and the genus ''[[Bengalia]]'' are known to steal food carried by ants.<ref>{{cite book|last1=Marshall |first1=S.A. |title=Manual of Afrotropical Diptera. Volume 1. Introductory chapters and keys to Diptera families. Suricata 4. |last2=Kirk-Spriggs |first2=A.H. |publisher=South African National Biodiversity Institute|year=2017|editor1=Kirk-Spriggs, A.H. |place=Pretoria |pages=135–152 |chapter=Natural history of Diptera |editor2=Sinclair, B.J.}}</ref> Adults of ''[[Ephydra hians]]'' forage underwater, and have special hydrophobic hairs that trap a bubble of air that lets them breathe underwater.<ref>{{Cite journal |last1=van Breug |first1=Floris |last2=Dickinson|first2=Michael H. |date=2017 |title=Superhydrophobic diving flies ( Ephydra hians ) and the hypersaline waters of Mono Lake |journal=Proceedings of the National Academy of Sciences |volume=114 |issue=51 |pages=13483–13488 |doi=10.1073/pnas.1714874114 |pmc=5754803 |pmid=29158381 |bibcode=2017PNAS..11413483V |doi-access=free}}</ref>

=== Anti-predator adaptations ===

{{Further|Anti-predator adaptation}}

[[File:Grosser Wollschweber Bombylius major.jpg|thumb|The large bee-fly, ''[[Bombylius major]]'', is a [[Batesian mimic]] of bees, and a bee [[Parasitism|parasite]], feeding on larvae.]]

Flies are eaten by other animals at all stages of their development. The eggs and larvae are parasitised by other insects and are eaten by many creatures, some of which specialise in feeding on flies but most of which consume them as part of a mixed diet. Birds, bats, frogs, lizards, dragonflies and spiders are among the predators of flies.<ref name=Collins>{{cite book |last=Collins |first=Robert |title=What eats flies for dinner? |url=https://books.google.com/books?id=OR_KmAEACAAJ |year=2004 |publisher=Shortland Mimosa |isbn=978-0-7327-3471-8}}</ref> Many flies have evolved [[mimicry|mimetic resemblances]] that aid their protection. [[Batesian mimicry]] is widespread with many hoverflies resembling bees and wasps,<ref>{{cite book |last1=Gilbert |first1=Francis |title=The evolution of imperfect mimicry in hoverflies |url=http://eprints.nottingham.ac.uk/96/1/ImperfectMimicry.pdf |publisher=CABI |date=2004 |access-date=27 July 2016 |archive-date=17 November 2017 |archive-url=https://web.archive.org/web/20171117175346/http://eprints.nottingham.ac.uk/96/1/ImperfectMimicry.pdf }}</ref><ref>{{cite journal |doi=10.1093/beheco/arn148 |title=Do hoverflies (Diptera: Syrphidae) sound like the Hymenoptera they morphologically resemble? |journal=Behavioral Ecology |volume=20 |issue=2 |pages=396–402 |year=2008 |last1=Rashed |first1=A. |last2=Khan |first2=M. I. |last3=Dawson |first3=J. W. |last4=Yack |first4=J. E. |last5=Sherratt |first5=T. N.|doi-access=free }}</ref> ants<ref>{{cite journal |doi=10.1076/snfe.37.1.19.2114 |title=Male-male agonistic behavior and ant-mimicry in a Neotropical richardiid (Diptera: Richardiidae) |journal=Studies on Neotropical Fauna and Environment |volume=37 |pages=19–22 |year=2002 |last1=Pie |first1=Marcio R. |last2= Del-Claro |first2=Kleber|issue=1 |bibcode=2002SNFE...37...19P |s2cid=84201196 }}</ref> and some species of tephritid fruit fly resembling spiders.<ref>{{cite journal |doi=10.1093/aesa/81.3.532 |title=Spider mimicry in fruit flies (Diptera: Tephritidae): Further experiments on the deterrence of jumping spiders (Araneae: Salticidae) by ''Zonosemata vittigera'' (Coquillett) |journal=Annals of the Entomological Society of America |volume=81 |issue=3 |pages=532–536 |year=1988 |last1=Whitman |first1=D. W. |last2=Orsak |first2=L. |last3=Greene |first3=E.}}</ref> Some species of hoverfly are [[myrmecophilous]]—their young live and grow within the nests of ants. They are protected from the ants by imitating chemical odours given by ant colony members.<ref>{{cite journal |title=Ant hosts of ''Microdon'' (Diptera: Syrphidae) in the Pacific Northwest | first1=Roger D. |last1= Akre | first2=William B. |last2=Garnett |first3=Richard S. |last3= Zack | journal=Journal of the Kansas Entomological Society | volume=63 | issue=1 |year=1990 | pages=175–178 | jstor=25085158 }}</ref> Bombyliid bee flies such as ''[[Bombylius major]]'' are short-bodied, round, furry, and distinctly bee-like as they visit flowers for nectar, and are likely also Batesian mimics of bees.<ref name="Godfray1994">{{cite book |last=Godfray |first=H. C. J. |title=Parasitoids: Behavioral and Evolutionary Ecology |url=https://archive.org/details/parasitoidsbehav0000godf |url-access=registration |year=1994 |publisher=Princeton University Press |isbn=978-0-691-00047-3 |page=[https://archive.org/details/parasitoidsbehav0000godf/page/299 299]}}</ref>

In contrast, ''[[Drosophila subobscura]],'' a species of fly in the genus ''[[Drosophila]]'', lacks a category of hemocytes that are present in other studied species of ''[[Drosophila]]'', leading to an inability to defend against parasitic attacks, a form of innate immunodeficiency.<ref>{{Cite journal |last1=Eslin |first1=Patrice |last2=Doury |first2=Géraldine |date=2006 |title=The fly Drosophila subobscura: A natural case of innate immunity deficiency |journal=Developmental & Comparative Immunology |volume=30 |issue=11 |pages=977–983 |doi=10.1016/j.dci.2006.02.007 |pmid=16620975}}</ref>

== Human interaction and cultural depictions ==
{{further |Human interactions with insects}}

===Symbolism===
[[File:Christus carthusian.jpg|thumb|left|upright |[[Petrus Christus]]'s 1446 painting ''Portrait of a Carthusian'' has a ''musca depicta'' (painted fly) on a ''[[trompe-l'œil]]'' frame.]]

Flies play a variety of symbolic roles in different cultures. These include both positive and negative roles in religion. In the traditional [[Navajo]] religion, Big Fly is an important spirit being.<ref>{{cite book |title=Handbook of North American Indians |chapter-url=http://www.users.humboldt.edu/jwpowell/LelandWymanHONAI-NavajoCeremonialSystem,reduced.pdf |page=539 |chapter=Navajo Ceremonial System |last=Wyman |first=Leland Clifton |year=1983 |quote=Nearly every element in the universe may be thus personalized, and even the least of these such as tiny Chipmunk and those little insect helpers and mentors of deity and man in the myths, Big Fly (''Dǫ'soh'') and Ripener (Corn Beetle) Girl (''<nowiki />'Anilt'ánii 'At'ééd'') (Wyman and Bailey 1964:29–30, 51, 137–144), are as necessary for the harmonious balance of the universe as is the great Sun. |access-date=30 July 2015 |archive-url=https://web.archive.org/web/20160305073542/http://www.users.humboldt.edu/jwpowell/LelandWymanHONAI-NavajoCeremonialSystem,reduced.pdf |archive-date=5 March 2016 }}</ref><ref>{{cite book |last1=Wyman |first1=Leland Clifton |last2=Bailey  |first2=Flora L. |title=Navaho Indian Ethnoentomology|series=Anthropology Series |issue=12–13 |url=https://books.google.com/books?id=tHl1AAAAMAAJ&q=Big+Fly |date=1964 |publisher=University of New Mexico Press |isbn=978-0-8263-0110-9 |lccn=64024356}}</ref><ref>{{cite web |url=http://www.native-languages.org/legends-fly.htm |title=Native American Fly Mythology |publisher=Native Languages of the Americas website}}</ref> In [[Christian demonology]], [[Beelzebub]] is a demonic fly, the "Lord of the Flies", and a god of the [[Philistine]]s.<ref>"Βεελζεβούλ, ὁ indecl. (v.l. Βεελζεβούβ and Βεεζεβούλ W-S. §5, 31, cp. 27 n. 56) Beelzebul, orig. a Philistine deity; the name בַּעַל זְבוּב means Baal (lord) of the flies (4 Km 1:2, 6; Sym. transcribes βεελζεβούβ; Vulgate Beelzebub; TestSol freq. Βεελζεβούλ,-βουέλ).", Arndt, W., Danker, F. W., & Bauer, W. (2000). A Greek-English lexicon of the New Testament and other early Christian literature (3rd ed.) (173). Chicago: University of Chicago Press.</ref><ref>"1. According to 2 Kgs 1:2–6 the name of the Philistine god of Ekron was Lord of the Flies (Heb. ba'al zeaûḇ), from whom Israel's King Ahaziah requested an oracle.", Balz, H. R., & Schneider, G. (1990–). Vol. 1: Exegetical dictionary of the New Testament (211). Grand Rapids, Mich.: Eerdmans.</ref><ref>"For etymological reasons, Baal Zebub must be considered a Semitic god; he is taken over by the Philistine Ekronites and incorporated into their local cult.", Herrmann, "Baal Zebub", in Toorn, K., Becking, B., & Horst, P. W. (1999). Dictionary of deities and demons in the Bible DDD (2nd extensively rev. ed.) (154). Leiden; Boston; Grand Rapids, Mich.: Brill; Eerdmans.</ref>

Flies have appeared in literature since ancient [[Sumer]].<ref name="BlackGreen1992">{{cite book |last1=Black |first1=Jeremy |first2=Anthony |last2=Green |title=Gods, Demons and Symbols of Ancient Mesopotamia: An Illustrated Dictionary |url=https://books.google.com/books?id=05LXAAAAMAAJ&q=Inana |publisher=[[The British Museum Press]] |year=1992 |isbn=978-0-7141-1705-8 |pages=84–85}}</ref> In a Sumerian poem, a fly helps the goddess [[Inanna]] when her husband [[Dumuzid]] is being chased by ''[[Gallu|galla]]'' demons.<ref name="BlackGreen1992"/> In the Mesopotamian versions of the [[flood myth]], the dead corpses floating on the waters are compared to flies.<ref name="BlackGreen1992"/> Later, the gods are said to swarm "like flies" around the hero [[Utnapishtim]]'s offering.<ref name="BlackGreen1992"/> Flies appear on [[Babylonia|Old Babylonian]] seals as symbols of [[Nergal]], the god of death.<ref name="BlackGreen1992"/> Fly-shaped [[lapis lazuli]] beads were often worn in ancient Mesopotamia, along with other kinds of fly-jewellery.<ref name="BlackGreen1992"/>

In Ancient Egypt, flies appear in amulets and as a military award for bravery and tenacity, due to the fact that they always come back when swatted at. It is thought that flies may have also been associated with the departing spirit of the dead, as they are often found near dead bodies. In modern Egypt, a similar belief persists in some areas to not swat at shiny green flies, as they may be carrying the soul of a recently deceased person.<ref>{{Cite book |last=Haynes |first=Dawn |url=https://scholar.sun.ac.za/bitstream/10019.1/79920/1/haynes_symbolism_2013.pdf |title=The Symbolism and Significance of the Butterfly in Ancient Egypt}}</ref>

In a little-known [[Greek myth]], a very chatty and talkative maiden named [[Myia (mythology)|Myia]] (meaning "fly") enraged the moon-goddess [[Selene]] by attempting to seduce her lover, the sleeping [[Endymion (mythology)|Endymion]], and was thus turned by the angry goddess into a fly, who now always deprives people of their sleep in memory of her past life.<ref>{{cite book | title = Metamorphosis in Greek Myths | first = Paul M. C. | last = Forbes Irving | publisher = [[Clarendon Press]] | date = 1990 | url = https://books.google.com/books?id=URvXAAAAMAAJ | isbn = 0-19-814730-9 | location = Oxford | page = 315}}</ref><ref>{{cite book | page = [https://books.google.com/books?id=oNWFDk5mOvQC&pg=PA5 5] | title = Lucian: Selected Dialogues | author1 = Lucian | author2 = C. D. N. Costa | author-link1 = Lucian | location = Oxford, New York | date = 2005 | publisher = [[Oxford University Press]] | url = https://books.google.com/books?id=oNWFDk5mOvQC | isbn = 978-0-19-925867-3}}</ref> In ''[[Prometheus Bound]]'', which is attributed to the Athenian tragic playwright [[Aeschylus]], a [[horse-fly|gadfly]] sent by [[Zeus]]'s wife [[Hera]] pursues and torments his mistress [[Io (mythology)|Io]], who has been transformed into a cow and is watched constantly by the hundred eyes of the herdsman [[Argus Panoptes|Argus]]:<ref>{{cite book |last1=Belfiore |first1=Elizabeth S. |title=Murder among Friends: Violation of Philia in Greek Tragedy |date=2000 |publisher=[[Oxford University Press]] |location=Oxford, England |isbn=978-0-19-513149-9 |page=47 |url=https://books.google.com/books?id=zhqCDBBEXSkC&q=Prometheus+Bound+Io+gadfly&pg=PA47}}</ref><ref name="Stagman2010">{{cite book |last=Stagman |first=Myron |title=Shakespeare's Greek Drama Secret |url=https://books.google.com/books?id=encnBwAAQBAJ&pg=PA207 |date=11 August 2010 |publisher=Cambridge Scholars Publishing |isbn=978-1-4438-2466-8 |pages=205–208}}</ref> "Io: Ah! Hah! Again the prick, the stab of gadfly-sting! O earth, earth, hide, the hollow shape—Argus—that evil thing—the hundred-eyed."<ref name="Stagman2010"/> [[William Shakespeare]], inspired by Aeschylus, has [[Tom o'Bedlam]] in ''[[King Lear]]'', "Whom the foul fiend hath led through fire and through flame, through ford and whirlpool, o'er bog and quagmire", driven mad by the constant pursuit.<ref name="Stagman2010"/> In ''[[Antony and Cleopatra]]'', Shakespeare similarly likens Cleopatra's hasty departure from the [[Battle of Actium|Actium battlefield]] to that of a cow chased by a gadfly.<ref name="Walker2002">{{cite book |last=Walker |first=John Lewis |title=Shakespeare and the Classical Tradition: An Annotated Bibliography, 1961–1991 |url=https://books.google.com/books?id=q3Voi0Dk_HwC&pg=PA363 |year=2002 |publisher=Taylor & Francis |isbn=978-0-8240-6697-0 |page=363}}</ref> More recently, in 1962 the biologist Vincent Dethier wrote ''To Know a Fly'', introducing the general reader to the behaviour and physiology of the fly.<ref>{{cite book |last1=Dethier |first1=Vincent G. |title=To Know a Fly |url=https://archive.org/details/toknowfly00deth |url-access=registration |date=1962 |publisher=Holden-Day |location=San Francisco}}</ref>

''[[Musca depicta]]'' ("painted fly" in Latin) is a depiction of a fly as an inconspicuous element of various paintings. This feature was widespread in 15th and 16th centuries paintings and its presence may be explained by various reasons.<ref name=eoi>''Encyclopedia of Insects'', [https://books.google.com/books?id=Jk0Hym1yF0cC&dq=%22musca+depicta%22&pg=PA242 p. 242]</ref>

Flies appear in popular culture in concepts such as [[fly-on-the-wall]] [[documentary]]-making in [[filmmaking|film]] and [[television production]]. The [[metaphor]]ic name suggests that events are seen [[Candid photography|candidly]], as a fly might see them.<ref>{{cite web |url=http://www.screenonline.org.uk/tv/id/698785/ |publisher=British Film Institute |title=Fly on the Wall |access-date=21 July 2016}}</ref> Flies have inspired the design of miniature flying robots.<ref>{{cite journal |last1=Ma |first1=Kevin Y. |last2=Chirarattananon |first2=Pakpong |last3=Fuller |first3=Sawyer B. |last4=Wood |first4=Robert J. |date=2013-05-03 |title=Controlled flight of a biologically inspired, insect-scale robot |journal=Science |volume=340 |issue=6132 |pages=603–607 |doi=10.1126/science.1231806 |pmid=23641114|bibcode=2013Sci...340..603M |s2cid=21912409 }}</ref> [[Steven Spielberg]]'s 1993 film ''[[Jurassic Park]]'' relied on the idea that [[DNA]] could be preserved in the stomach contents of a blood-sucking fly [[fossil]]ised in [[amber]], though the mechanism has been discounted by scientists.<ref>{{cite news |last1=Gray |first1=Richard |title=Jurassic Park ruled out – dinosaur DNA could not survive in amber |url=https://www.telegraph.co.uk/news/science/dinosaurs/10303795/Jurassic-Park-ruled-out-dinosaur-DNA-could-not-survive-in-amber.html |access-date=21 July 2016 |agency=Daily Telegraph |date=12 September 2013}}</ref>

===Economic importance===
[[File:Anopheles stephensi.jpeg|thumb|An ''[[Anopheles stephensi]]'' mosquito drinking human blood. The species carries [[malaria]].]]

Dipterans are an important group of insects and have a considerable impact on the environment. Some [[leaf-miner flies]] (Agromyzidae), [[Tephritidae|fruit flies]] (Tephritidae and Drosophilidae) and [[gall midges]] (Cecidomyiidae) are pests of agricultural crops; others such as [[tsetse flies]], [[screwworm]] and [[botflies]] (Oestridae) attack livestock, causing wounds, spreading disease, and creating significant economic harm. See article: [[Parasitic flies of domestic animals]]. A few can even cause [[myiasis]] in humans. Still others such as [[mosquito]]es (Culicidae), [[Black fly|blackflies]] (Simuliidae) and [[drain flies]] (Psychodidae) impact human health, acting as [[Vector (epidemiology)|vectors]] of major tropical diseases.
Among these, ''[[Anopheles]]'' mosquitoes transmit [[malaria]], [[filariasis]], and [[arboviruses]]; ''[[Aedes aegypti]]'' mosquitoes carry [[dengue fever]] and the [[Zika virus]]; blackflies carry [[river blindness]]; sand flies carry [[leishmaniasis]]. Other dipterans are a nuisance to humans, especially when present in large numbers; these include houseflies, which contaminate food and spread food-borne illnesses; the [[Ceratopogonidae|biting midges and sandflies]] (Ceratopogonidae) and the [[Muscidae|houseflies and stable flies]] (Muscidae).<ref name=Resh>{{cite book |last1=Resh |first1=Vincent H. |last2=Cardé |first2=Ring T. |title=Encyclopedia of Insects |url=https://books.google.com/books?id=Jk0Hym1yF0cC&pg=PA284 |year=2009 |publisher=Academic Press |isbn=978-0-08-092090-0 |pages=284–297}}</ref> In tropical regions, eye flies ([[Chloropidae]]) which visit the eye in search of fluids can be a nuisance in some seasons.<ref>{{Cite journal |last1=Mulla |first1=Mir S. |last2=Chansang |first2=Uruyakorn |title=Pestiferous nature, resting sites, aggregation, and host-seeking behavior of the eye fly ''Siphunculina funicola'' (Diptera: Chloropidae) in Thailand |journal=Journal of Vector Ecology |volume=32 |issue=2 |doi=10.3376/1081-1710(2007)32[292:pnrsaa]2.0.co;2 |pages=292–301 |year=2007 |pmid=18260520 |s2cid=28636403 }}</ref>

Many dipterans serve roles that are useful to humans. Houseflies, blowflies and [[Mycetophilidae|fungus gnats]] (Mycetophilidae) are scavengers and aid in decomposition. [[Robber flies]] (Asilidae), [[Tachinidae|tachinids]] (Tachinidae) and [[Empididae|dagger flies and balloon flies]] (Empididae) are predators and parasitoids of other insects, helping to control a variety of pests. Many dipterans such as [[bee flies]] (Bombyliidae) and [[hoverflies]] (Syrphidae) are [[Pollination|pollinators]] of crop plants.<ref name=Resh/>

=== Uses ===
[[File:Researcher beside Vials closed by cotton plugs and filled with Fruit fly larvae.jpg|thumb|left|Diptera in research: ''[[Drosophila melanogaster]]'' fruit fly larvae being bred in tubes in a [[genetics]] laboratory]]

''[[Drosophila melanogaster]]'', a fruit fly, has long been used as a [[model organism]] in research because of the ease with which it can be bred and reared in the laboratory, its small [[genome]], and the fact that many of its genes have counterparts in higher [[eukaryote]]s. A large number of genetic studies have been undertaken based on this species; these have had a profound impact on the study of [[gene expression]], [[Regulation of gene expression|gene regulatory mechanisms]] and [[mutation]]. Other studies have investigated [[physiology]], [[Pathogenesis|microbial pathogenesis]] and development among other research topics.<ref>{{cite web |url=https://www.yourgenome.org/theme/fruit-flies-in-the-laboratory/ |title=Fruit flies in the laboratory |date=19 June 2015 |website=YourGenome |access-date=24 March 2025}}</ref> The studies on dipteran relationships by [[Willi Hennig]] helped in the development of [[cladistics]], techniques that he applied to morphological characters but now adapted for use with molecular sequences in phylogenetics.<ref>{{Cite journal |last=Ashlock |first=P. D. |date=1974 |title=The Uses of Cladistics |journal=Annual Review of Ecology and Systematics |volume=5 |issue=1 |pages=81–99 |doi=10.1146/annurev.es.05.110174.000501 |bibcode=1974AnRES...5...81A }}</ref>

[[Maggot]]s found on corpses are useful to [[forensic entomology|forensic entomologists]]. Maggot species can be identified by their anatomical features and by matching their [[DNA]]. Maggots of different species of flies visit corpses and carcases at fairly well-defined times after the death of the victim, and so do their predators, such as beetles in the family [[Histeridae]]. Thus, the presence or absence of particular species provides evidence for the time since death, and sometimes other details such as the place of death, when species are confined to particular habitats such as [[woodland]].<ref>{{cite journal |last1=Joseph |first1=Isaac |last2=Mathew |first2=Deepu G. |last3=Sathyan |first3=Pradeesh |last4=Vargheese |first4=Geetha |title=The use of insects in forensic investigations: An overview on the scope of forensic entomology |journal=Journal of Forensic Dental Sciences |date=2011 |volume=3 |issue=2 |pages=89–91 |doi=10.4103/0975-1475.92154 |pmc=3296382 |pmid=22408328 |doi-access=free }}</ref>

[[File:Casu Marzu cheese.jpg|thumb|right|[[Casu marzu]] is a traditional [[Sardinia]]n sheep milk cheese that contains larvae of the [[cheese fly]], ''Piophila casei''.]]

Some species of maggots such as [[Calliphoridae|blowfly larvae (gentles)]] and bluebottle larvae ([[caster (maggot)|casters]]) are bred commercially; they are sold as [[fishing bait|bait]] in [[angling]], and as food for carnivorous animals (kept as pets, in zoos, or for research) such as some [[mammal]]s,<ref>{{cite journal |last1=Ogunleye |first1=R. F. |last2=Edward |first2=J. B. |title=Roasted maggots (Dipteran larvae) as a dietary protein source for laboratory animals |journal=African Journal of Applied Zoology and Environmental Biology |date=2005 |volume=7 |pages=140–143 |url=http://www.ajol.info/index.php/ajazeb/article/view/41163}}</ref> [[fish]]es, [[reptile]]s, and [[bird]]s. It has been suggested that fly larvae could be used at a large scale as food for farmed chickens, pigs, and fish. However, consumers are opposed to the inclusion of insects in their food, and the use of insects in animal feed remains illegal in areas such as the [[European Union]].<ref>{{cite web |last1=Fleming |first1=Nic |title=How insects could feed the food industry of tomorrow |url=http://www.bbc.com/future/story/20140603-are-maggots-the-future-of-food |publisher=[[British Broadcasting Corporation]] |access-date=24 May 2016 |date=4 June 2014}}</ref><ref>{{cite web |title=Why are insects not allowed in animal feed? |url=http://www.protix.eu/wp-content/uploads/2014/07/20141029_Why-are-insects-not-allowed-in-animal-feed_Whitepaper_Insect_meal.pdf |publisher=All About Feed |access-date=24 May 2016 |date=August 2014 |archive-url=https://web.archive.org/web/20160811001146/http://www.protix.eu/wp-content/uploads/2014/07/20141029_Why-are-insects-not-allowed-in-animal-feed_Whitepaper_Insect_meal.pdf |archive-date=11 August 2016 }}</ref> 

Fly larvae can be used as a [[biomedical]] tool for wound care and treatment. [[Maggot debridement therapy]] (MDT) is the use of [[Calliphoridae|blow fly]] larvae to remove the dead tissue from wounds, most commonly being amputations. Historically, this has been used for centuries, both intentional and unintentional, on battlefields and in early hospital settings.<ref>{{Cite journal |last1=Stegman |first1=Sylvia |last2=Steenvoorde |first2=Pascal |date=2011 |title=Maggot debridement therapy |url=https://www.researchgate.net/publication/260701991 |journal=Proceedings of the Netherlands Entomological Society Meeting |volume=22 |pages=61–66 }}</ref> Removing the dead tissue promotes cell growth and healthy wound healing. The larvae also have [[biochemical]] properties such as [[antibacterial]] activity found in their secretions as they feed.<ref>{{Cite journal |last1=Diaz-Roa |first1=A. |last2=Gaona |first2=M. A. |last3=Segura |first3=N. A. |last4=Suárez |first4=D. |last5=Patarroyo |first5=M.A. |last6=Bello |first6=F. J. |date=August 2014 |title=''Sarconesiopsis magellanica'' (Diptera: Calliphoridae) excretions and secretions have potent antibacterial activity |journal=Acta Tropica |pages=37–43 |doi=10.1016/j.actatropica.2014.04.018 |pmid=24754920 |volume=136 |url=https://repository.urosario.edu.co/handle/10336/23597 }}</ref> These medicinal maggots are a safe and effective treatment for chronic wounds.<ref>{{Cite journal |last1=Gilead |first1=L. |last2=Mumcuoglu |first2=K. Y. |last3=Ingber |first3=A. |date=16 August 2013 |title=The use of maggot debridement therapy in the treatment of chronic wounds in hospitalised and ambulatory patients |journal=Journal of Wound Care |doi=10.12968/jowc.2012.21.2.78 |pmid=22584527 |volume=21 |issue=2 |pages=78–85}}</ref>

The [[Sardinia]]n cheese [[casu marzu]] is exposed to flies known as [[cheese skipper]]s such as ''[[Piophila casei]]'', members of the family [[Piophilidae]].<ref>{{cite journal |year=2007 |title=A mite unappetizing |url=http://www.entsoc.org/PDF/Pubs/Periodicals/AE/AE-2007/Fall/Buzzwords.pdf |archive-url=https://web.archive.org/web/20101216084837/http://entsoc.org/PDF/Pubs/Periodicals/AE/AE-2007/Fall/Buzzwords.pdf |archive-date=2010-12-16 |journal=American Entomologist |volume=53 |issue=3 |pages=132–133 |last=Berenbaum |first=May |doi=10.1093/ae/53.3.132 }}</ref> The digestive activities of the fly larvae soften the cheese and modify the aroma as part of the process of maturation. At one time European Union authorities banned sale of the cheese and it was becoming hard to find,<ref>{{cite web |last1=Colangelo |first1=Matt |title=A Desperate Search for Casu Marzu, Sardinia's Illegal Maggot Cheese |url=http://www.foodandwine.com/fwx/desperate-search-casu-marzu-sardinias-illegal-maggot-cheese |publisher=Food and Wine |access-date=24 May 2016 |date=9 October 2015}}</ref> but the ban has been lifted on the grounds that the cheese is a traditional local product made by traditional methods.<ref>{{cite news |title=Illegal food: step away from the cheese, ma'am |last=Brones |first=Anna |url=https://www.theguardian.com/lifeandstyle/wordofmouth/2013/apr/15/illegal-food-cheese-us-mimolette |newspaper=[[The Guardian]] |date=15 April 2013 |access-date=26 May 2016}}</ref>

== Notes ==

{{notelist}}

== References ==

{{reflist|30em}}

== Further reading ==

* Blagoderov, V.A., Lukashevich, E.D. & Mostovski, M.B. (2002)). "[http://palaeoentomolog.ru/New/diptera.html Order Diptera]". In: [[Alex Rasnitsyn|Rasnitsyn, A.P.]] and Quicke, D.L.J. ''The History of Insects'', Kluwer pp.–227–240.<!--on Evolution-->
* Colless, D.H. & McAlpine, D.K. (1991). ''Diptera (flies)'', pp.&nbsp;717–786. In: The Division of Entomology. Commonwealth Scientific and Industrial Research Organisation, Canberra (spons.), ''The Insects of Australia''. Melbourne University Press.
* [[Willi Hennig|Hennig, Willi]]. "Diptera (Zweifluger)". ''Handb. Zool. Berl''. 4 (2) (31):1–337. General introduction with key to World Families {{In lang|de}}.
* [[Harold Oldroyd|Oldroyd, Harold]] (1965). ''The Natural History of Flies''. W. W. Norton.
* [[Eugène Séguy|Séguy, Eugène]] (1924–1953). ''Diptera: recueil d'etudes biologiques et systematiques sur les Dipteres du Globe'' (Collection of biological and systematic studies on Diptera of the World). 11 vols. ''Part of Encyclopedie Entomologique'', Serie B II: Diptera.
* Séguy, Eugène (1950). ''La Biologie des Dipteres''.
* {{cite web |last=Thompson |first=F. Christian |title=Sources for the Biosystematic Database of World Diptera (Flies) |publisher=[[United States Department of Agriculture]], Systematic Entomology Laboratory |url=http://www.sel.barc.usda.gov/diptera/names/BDWDsour.pdf |archive-url=https://web.archive.org/web/20150918204612/http://www.sel.barc.usda.gov/diptera/names/BDWDsour.pdf |archive-date=18 September 2015 |ref=none}}

== External links ==

{{Wikiquote|Flies}}
{{Commons category|Diptera}}
{{Wikispecies |Diptera}}

'''General'''
* [http://www.diptera.info The Diptera.info portal with galleries and discussion forums]
* [http://wwx.inhs.illinois.edu/research/flytree/ FLYTREE – dipteran phylogeny]. {{Webarchive|url=https://web.archive.org/web/20200413095925/https://www.inhs.illinois.edu/research/flytree/ |date=13 April 2020 }}.
* [http://www.dipteristsforum.org.uk/ The Dipterists Forum] – The Society for the study of flies
* [http://bugguide.net/node/view/55 BugGuide (USA and Canada)]
* [http://hbs.bishopmuseum.org/fossilcat/ The World Catalog of Fossil Diptera]
* [http://tolweb.org/tree?group=Diptera The Tree of Life Project]

'''Anatomy'''
* [https://ento.csiro.au/biology/fly/fly_atlas.html Anatomical Atlas of Flies at CSIRO]
* [http://www.drawwing.org/insects/diptera DrawWing venation - identification aid]

'''Describers'''
* [http://hbs.bishopmuseum.org/publications/pdf/tr51.pdf Authors of fly names] (PDF)

{{Diptera}}
{{Orders of Insects}}
{{Insects in culture}}
{{Taxonbar|from=Q25312}}
{{Authority control}}

[[Category:Flies| ]]
[[Category:Diptera by classification| ]]
<!-- [[Category:Pollinators]] not all pollinators -->
[[Category:Anisian first appearances]]
[[Category:Extant Middle Triassic first appearances]]
[[Category:Insects in culture]]
[[Category:Animal taxa named by Carl Linnaeus]]
[[Category:Triassic animals of North America]]
[[Category:Triassic animals of South America]]
[[Category:Triassic insects]]